Selector testing circuit



July 28, 1931.

N. G. PALMGREN SELECTOR TESTING CIRCUIT Filed March 29, 1929 Patented July 28, 1931 UNITED STATES PATENT OFFICE Nits GNNAN. TALMGREN, or sToCKHoLivI, swEDnN, AssIGNoR To TELEFON AKTIE- BQLAGET L. IvI. ERICSSON, or STOCKHOLM, swnDEN, A CoMraNY or SWEDEN SELECTOR TESTING CIRCUIT vf Application led March 29, 1929, Serial No. 351,052, and in Sweden March 24, 1928.

In automatic telephone exchanges incorrect connections sometimes are caused by the fact that a selector hunting for a free junction line is passing over the Contacts of a junction line in the moment of interruption of a previously completed talking connection `over said j unction line. Such incorrect connections have a tendency to -Cccur especially in such systems in which therestoration is initiated by the interruption of a circuit overthe private wiper of the selector and the third wire. A selector passing over the contact appertaining to a junction line included in a talking connection in the moment of interruption may namely then prevent the interruption of said circuit as the latter instead is closed over the private wiper of said selector and the appertaining testing relay, the hunting selector being thus stopped land the restoration of the succeeding f selectors in the talking connection prevented.

The objectof the present invention is to elimv inate` incorrect connections of said kind and consists substantially therein that the resistance in that portion of the testing circuit in question which belongs to a free junction line,

after completed testing and connection into circuit, will be increased to a value which per vse is suflicient to prevent the connection of anotherselector to the already engaged junction line independent of the changes Whichafterwards may occur in other parts of the testing circuit by way of example upon interruption of the talking connection. j

The invention will be more closely described with reference to the accompanying set under the control of registers. The select-r j ors are assumed to have two setting motions in the same plane i. e.k a rotating motion to select a certain contact row and also a radial motion to select a line within the Contact row. It is further assumed that the selectors are of that type in which the appertaining contact bank consists of bare wires a, Z9, c which to the junction line.

extend perpendicularly to the plane of motion of the contact arms through a plurality of selectors. During their rotating motion the Contact arms move outside the wire bank and during the succeeding radial motion they move into the space between the wires a, b, on the one side, and the wire c, on the other side. The selectors are power driven in known manner under the control of two clutch magnets MHG and MVG and two control magnets CVG and CRG the turning motion being then produced by a simultaneous energization of the magnets MHG and GVG whereas the radial motion is effected by a simultaneous energization of the magnet MHG and CBG. At the restoration, the clutch magnet MVG co-operates in a similar manner with a magnet CRG and CVG. The group selectors are further provided with throw-over switches VO and RO the former of which is shifted when the selector leaves its normal position and is returned to the position shown on the drawing upon the restoration of the selector whereasthe latter is shifted when the Contact arm begins its radial movement and is returned to the position shown on the drawing upon the return to the starting position of the radial motion.

The connection to a calling subscribers line can be brought about in a manner known per se by means of a call finder AS of substantially the same design as the group selectors.

1 The system functions substantially as follows. After the calling subscribers liney has been connected to a junction line FL1 through the call nder AS a free register RR is connected in known manner through a finder RS The register is only shown diagrammatically as its function does not need to be described in detail in this connection. A sequence switch not shown on the` drawing i and appertaining to the unction line FL1 in this moment closes a circuit l over a contact 7c in said sequence switch through a relay R0G3 and two ohmic re sistances R1 and R2. After the register is set according to the desired number a circuit 2 is closed through a relay RIG2 which locks itself over the contact 3 and at the same time closes a circuit 4 through a relay RlGl of high resistance. TWhen thel latter relay is energized itlocks itself over its contact 5 and closes also a circuit 6 through the control magnet CVG which in turn closes a circuit 7 through the clutch magnet MHG. Thereby the selector is started. During the following rotating motion of the selector impulses are sent in known manner over a circuit 8 to the register' RR a .register switch being. thereby set in known manner. l/Vhen this register switch reaches a cert-ain setting position the circuit 2 is interrupted the relay RlGg being then de-energized. The latter relay interrupts the circuit 8 and opens the contact 9 in the circuit 6, the control magnet CVG and, as a consequence, also the clutch magnet MHG being then cle-energized so that the selector is stopped. Then a circuit 10 is closed through the control magnet CRG which in turn closes the circuit 11 through the clutch magnet MHG. As a consequence, the selector is started in radial direction to huntV for a free junctionline in the selected contact row. `Vhen the contact armsv make contact with a free junction line FL2 a testing` circuit 12 is closed over the testing contact @and through the non-inductive resistances R3, R4 corresponding to the resistances R1, R2. The testingcircuit containsY aY test-v ing relay B1G3 rwhich is'now energized, the'y circuit 10 of the clutch magnet CRV being then interrupted which results in that the selector stops. At the same time a circuit 13 is closed through a relay 'B1G andthe control magnet CVG. The relay B1G! has such a high resistance that the control magnet CVG then remains` inoperativel 0n the other hand, the relay B1G@ is energized then locking itself over the'contact A14E. rEhe relay R1G4 at its Contact 15 further short-circuits the winding GL of the testing relay R1G3 the current in theftesting circuit being then amplified to such a degree that the junction line PL2 is marked'as engaged through the drop of Voltage thus created at the testing contact c.

The winding GL is so wound that it counteracts the other winding HL of the testing relay. vThe objectof this arrangement is to render the testing relay comparatively' insensitive in the movement of testing in order to prevent a double connection in such cases when two group selectors simultanenously.

make Vcontact with the same junction line as the current then on account of the parallel connection of two testing yrelays to the same testing contact c becomesinsuihcient Ato start operation of any of the testing relays. By the short-circuiting of a counteracting winding both a reduction of the resistance in the testing Ycircuit and a large increase Vof the operative number of ampere-turns of the testing relay is gained which is ,important considering the other functions of the testing relay as will loe further described'in the following. By way of example, it may be mentioned that a satisfactory operation of the relay is obtained by providing HL with about 6,000 turns and the winding GL with 1,500 counteracting turns. The resistance R3 may then be about 250 ohms andthe resistance R4 about 150 ohms.

After the completed connection to the junction line FLZ a vcircuit 16 ,is closed .in .the register ,RR through `a relay rRG2 .in Vthe group selector GV2. Said relay isenergiZed and locks itself over its contact 17 and starts similar connections as the relay RlGZ. A re lay RZGl of a high resistance-and Acorresponding to the relay RIGl is thus connected into circuit over a contact 18 lofthe `relay1R2G2f`5he relay R2G1 then being energized vand loci-king itselfvover its contact 19. At thesame'timea circuit 20 is closed through-a controlm'agne't CVG which in turn closes Aarcircuit 21-through the clutch magnet MHG. The group selector GV2 thus starts its rotating motion lcurrent impulses being then VVsent over the5circuit22 to the register. When the corresponding register switch has been set in ajpreyi'ous'ly marked position the circuit 16 for the `rela-y E2G@ is interrupted the vselector y'being'then stopped. A circuit 423 is'then closed through the control magnet CBG and also'a circuit 24 through the clutchmagnetiMllS wherebythe selector is started in its radial motion to hunt fora free junction line EL3. When'the group selector finds such aline a current-path 25 is closed through the testing relay RZGS which is energizedandstops the selector at the same time as it closes a circuit k16 lfor Vthe relay R2G4. The latter relayloc'ks itself over its vContact 27 and 'short-circuits at -the same time over its contact28l the winding-GL of the relay RZGS. The'relays RZG and RGB are identical and serve the same purpose. The winding GL counteracts thus the vwinding HL and the short-circuiting'of thewinding GL marks the junction line FLS vkasengaged. The completion of the connection may thenY be performed in any 'arbitrary manner.

When the relay R2G1 wasenergizedit disconnected the branch wire including theresistance R4 in the testing circuitwhich `now instead is held closed over ithe relay E2G, As the latter relay hasa comparatively high resistance, by way of example 5501ohms, .the short circuit of the winding'GL ofthe testing relay R1G3 is thenfwitlhout any essential importance for the lmarking pof the-*junction line FL2 as engaged but 'the resistance in the winding of .therelay E2G1 `together with the resistance R3 is per se suflcient'to prevent a hunting selector to connect Vitself to said junction line. Y l

ylVhen the calling subscriber answersa contact 29 is closedin any known manner wherebythe testing relayRG3 is short-'circuitedL When thelatter relay, as a consequence,'is de- Said short-circuits remain for such a period of time as is required to transmit the call meter impulse. When the contact 29 is then reopened the testing relays E2G3 and R1G3 are again energized. Thanks to the short- Lcircuiting of the winding GL the testing relays are now supplied with a sufiicient current to be actuated in series with the relay R2G1`having .a high ohmic resistance or a correspondingrelay R3G1 in the selector appertaining to the junction lineFLS, respectively. v

When the subscriber again hooks up the receiver after a'inished call, initially, the group selector G1 is restored and then the successive selectors in turn. The restoration is started by that the contact 7c is interrupted the relay R1G1 then being cle-energized and closing. a circuit 34 through the control magnet CRG which in turn closes a circuit 35 through the clutch magnet MVG. This results in that the selector is now restored in radial direction. When the contact arms reach the starting position for the radial motion the switch RG1 is actuated the circuit for the control magnet CRG being then terrupted and the selector stops. At the same time, however, a circuit 3G is closed through the control magnet CVG which in turn closes a circuit 37 through the clutch magnet MVG the selector being thereby restored to the starting posit-ion in which the switch V01 is actuated so as to interrupt the circuit of the control magnet CVG andthe selector stops.

When the relay B1G1 was deenergized the circuit of the relay R1G4 was interrupted and also the circuit over the third Wire at the contact 3S of the relay R1G1 When the testing relay RlG is deenergized the group selector GVl is prepared to make a new connection. Upon the interruption of the circuit of the third wire also the relay R2G1 is deenergized which relay is establishing similar connections at the group selector GV2 as has been just described regarding the group selector GVl. B- said connections also the group selector TV2 is now restored.

It in that moment when the circuit l2 was interrupted at the contact 38, another group selectorA GV1 during the hunting -for a free junction line should pass the contacts appen taining to the junction line FL2 it is conceivable that the relay R2G1 is not de-energized because it should then he supplied over the testing magnet B1G3 in said selector said relay then being able to attract its armature and thus connects the selector to the junction line FL2. Such an incorrect connection' is, however, avoided, thereby that the relay RZG1 has such a high resistance that the testing relay llGs in the hunting selector is un able to attract its armature. Also the fact that the windings HL and GL in this moment are connected in series the testing relay thus having a. comparatively high resistance concurs to the sameresult. Thanks tothe series connection of the windings HL and GL the resistance of the testing relay is so high that it also prevents the relay R2G1 to remain energized while the hunting selector is still engaging the contacts in. question. The latter relay thus drops its armature in the same moment as the circuit of the third wire is interrupted at the contact 33. During the restoration ot' the selector GV2 also the branch wire containing the resistance R4 is interru ted at the contact 40, 41 of the switches V82 and R02. The testing contact c thus remains tensionless until the selector is completely restored. One is thus completely sure of that the restoration is not in any way disturbed by the operation of a selector which in the moment of connection is passing over the contacts of a junction line included in a talking connection.

T claim 1. In a telephone exchange system, a test circuit arrangement for selectors comprising a number of selectors, a number of junction lines, accessible to said selectors, a test circuit for each of said selectors extending over a movable Contact of the selector, a testrelay included in the selector section of said circuit, means under the control of said relay for reducing the resistance oi said part of the test circuit upon seizure ot an idle junction so as to provide a busy test potential 'for said junction, a test guard resistance, and means associated with the junction line and arranged to operate upon the seizure of the junction by a selector to connect said test lguard resistance into the junction section of the test circuit to increase the resistance oi the junction section of the test circuit so as to guard the junction after removal oi said busy test potential.

2. In a telephone exchange system, a test circuit arrangement for selectors comprising a number of selectors-r a number of junction lines, accessible to said selectors, a test circuit for each'of said selectors extending over a movable contact of the selector, a. test relay included in the selector section of said circuit, means under the control of said relay :tor reducing the resistance of said part of the test circuit upon seizure of an idle junction so as to provide a busy test potential for said junction, two branch circuits forming parallel branches of the junction section of the test circuit, one of said branches including annif-normal Contact .of aselector associated with the'junction line, a low resistance 1n the y branchlast mentioned, ahigh test guard resistanee in the other of said branches, and

n'ieans associated with the junction line and arranged to operateupon the seizure of the junction line by a selectorto connect said test guard resistance into circuit instead of said low resistance. f

8. In ya telephone exchange system, a test circuit arrangement forV selectors comprising a number of selectors, a number of junction lines, accessible to said selectors, a test circuitV for each of said selectors extending over a movable contact of the selector, aV test relay included in the selector section of said circuit, means under the control of said relay for reducing the resistance of said part of the test circuit upon seizure of an idle junction so as to provide a busy test potential for said junction, two branch circuits forming parallel branches of the junction section of tlie'test circuit, one of said branches including an ofl normal Contact of a selector associated with thev junction line, a low resistance in the branch last mentioned, a high test guard resistance in the other of said branches forming the winding of a relay, means associated with the junction line and arranged to operate upon the seizure of the unction line by a selector to connect said test guard resistance into circuit instead of said low resistance, and a front contact on said relay inv eluded in the test circuit so as to disconnect battery potential from the test circuit upon the cle-energizjation of said relay. l 4. In telephone exchange system, a test circuit arrangement t'or selectors comprising a number or" selectors, a number of junction lines, accessible to saidselectors, a test circuit for each of said selectors'extending over a movable contact of the selector, a test relay included in the selector section of said circuit and having two counteracting windings, means under the control of said relay for .shortcircuiting one of said windings thereby reducing the selector of the test Circuit soy as to provide busy test potential vlor said junction, a test guard resistance, and means associated with'the junction line and arranged to operate upon the seizure of the junction by a selector to connect sai'dtest guard resistance into the junction section of the test circuit to increase the resistance of the junction section of the test circuit so as to guard the junction after removal of said busy test potential.

yIii-testimony whereof I affix my signature'.

NILS GUNNAR PALMGREN. 

